The invention relates to a system for dosed conveying and selecting of cylindrical pellets for molding apparatus for lead frames.
A chip is mounted onto a central part of a lead frame intended for this purpose and the connecting points of the chip are connected with thin wires to the strip-like leads of the frame. Thereafter the leads and wiring are encapsulated with a protective plastic in a molding apparatus. In such molding apparatus pill or pellet-like units of plastic material are used which become plastic under temperature and pressure and are fed in this state to the lead frame situated in the mould cavity. The environment in which molding takes place is clean, a clean room or clean environment.
Due to the nature of the material the pellets are sources of contamination. This may be the result of crumbling of the pellet whereby dust formation and like contamination occur. It is therefore the object to keep the pellet, and particularly broken off pieces and other contaminating portions, outside the clean environment of the molding apparatus. Only pellets which can be properly processed, that is, without broken off fragments and the like, must be fed to the molding apparatus. On their way from a reservoir to the molding apparatus pellets can be damaged. The handling and transport must therefore take place very carefully.